C Program to convert lowercase to uppercase char array without using other functions available in the C standard library

I am trying to replace all lowercase letters by their uppercase counterpart without using other functions available in the C standard library and using pointers. I have my main.c:

#include <stdio.h>
#include "upper1.h"

int main() {
    
        char string[] = "HelloWorld";
        int arraySize = sizeof(string) / sizeof(string[0]);
        printf("String before transformation: ");
        int i;
        for (i= 0; i< arraySize; i++) {
            printf("%c", string[i]); //prints array information
        } 
        printf("\n");
        
        char *str = string; //pointer that points to the array
        
        upper1(str);
        
        printf("String before transformation: ");
        int j;
        for (j= 0; j< arraySize; j++) {
            printf("%c", string[i]); //prints array information
        } 
        printf("\n");
        
        return 0;
}

And I have my function code file:

void upper1(char *str) {
    int i;
    for(i = 0; i < 10; i++) {
        if(*str >= 65 + 32 && *str <= 90 + 32) { //65+32 is "a" and 90+32 is "z"
            *str = *str - 32;
        }
        str++;// skips one position of the array
    }
}

For some reason when I run I get:

gcc -g -Wall -c upper1.c -o upper1.o gcc -g -Wall -c main.c -o main.o gcc upper1.o main.o -o ex04 ./ex04 String before transformation: HelloWorld String before transformation: ��

Instead of

gcc -g -Wall -c upper1.c -o upper1.o gcc -g -Wall -c main.c -o main.o gcc upper1.o main.o -o ex04 ./ex04 String before transformation: HelloWorld String before transformation: HELLOWORLD

(I have a file "upper1.h" but that's correct only with: void upper1(char *str);)

Solution

It's because you're using i in your second loop instead of j.

printf("String before transformation: ");
int j;
for (j = 0; j < arraySize; j++) {
    printf("%c", string[j]); // use 'j' instead of 'i'
}

You can avoid a typo like this in the future by declaring your loop counter inside the for-loop. This ensures the counter is only accessible within the scope of the loop and can't be reused in another loop:

printf("String before transformation: ");
for (int j = 0; j < arraySize; j++) {
    printf("%c", string[j]);
}